Project Summary/Abstract Social interactions across the animal kingdom, from courtship rituals and aggressive interactions to spoken conversation, are wondrously complex - they necessarily involve back- and-forth feedback between nervous systems transmitted through multiple sensory modalities and each animal's behavior. Typical experiments in this field observe only a tiny fraction of the activity in any neuronal circuit, and then only under a very limited range of behavioral conditions. To overcome this limitation, the proposed research leverages the compact nervous system of Drosophila melanogaster, combined with its wealth of genetic tools, to study the dynamic behavioral interactions and detailed neural mechanisms that underlie courtship between males and females. The project combines unbiased measurement of behavior, neural circuit manipulations, neural recordings in behaving animals, and sophisticated computational models. The specific aims include: i) elucidating the computations that the brain performs during courtship by mapping the sensorimotor transformations underlying male and female interactions over time via quantitative behavioral assays and the generation of predictive models; ii) combining models with neural perturbations to map the underlying circuits that govern the link between sensory inputs and behaviors; And, iii) testing the models of neural control during courtship by monitoring neural activity in behaving animals experiencing fictive courtship stimuli in a virtual-reality apparatus. This work will substantially advance our understanding of how two interacting brains process and transfer information, and will uncover general principles of neural circuit function that will inform studies of sensorimotor integration in more complex animals, such as rodents and humans. The project will also produce new experimental and theoretical tools for studying social behaviors. Finally, it will shed light on the mechanisms that go awry in several disorders, including Autism Spectrum Disorder (ASD), in which sensory perception becomes disentangled from motor outputs ? these disorders have profound effects on cognitive well-being and a major impact on public health.